Commercial semiconductor foundries often limit designers to a few choices of materials or number of structural layers in a fabricated device. As a result it may not be possible to create many specialized devices required for demanding semiconductor or Micro Electro Mechanical Systems (MEMS) applications without custom fabrication methods, methods that are usually expensive to employ. As an alternative, highly complex structures can be made by flip-chip bonding of surface-micromachined features onto a variety of other substrates or even other chips fabricated in the same process. The original often silicon host substrate is then discarded during a following release etch to provide advanced MEMS devices that are suitable for RF, microwave, or optical applications where specific material properties or additional structural layers are required.
In recent years, the use of flip-chip assembly to create advanced MEMS devices has been shown to be a fast, reliable, simple and inexpensive method to produce highly planarized devices consisting of as many as five structural layers on virtually any desired substrate. This process has been demonstrated with a variety of micromirror arrays and variable capacitors fabricated atop ceramic substrates to achieve improved RF characteristics. Even more advanced micromirror arrays have been fabricated atop receiving modules prefabricated in a same processing run as the host module. Numerous styles of cantilever, torsion, and piston micromirror arrays have been demonstrated and these boast a variety of desirable characteristics. Mirror devices can for example achieve CMOS compatible low voltage addressing potentials or more than 3 micrometers of stable mechanical deflection since the mirror surfaces can rest as much as 10 micrometers above the substrate. Typical arrays have been designed with as much as 98.8% active surface area. Torsion and cantilever devices have demonstrated as much as 20 degrees of tilt using a variety of flexure arrangements to reduce needed electrical addressing potentials. The mirror surface of each such device is initially fabricated as the underside of a first releasable structural layer such that no topographical effects are induced. As a result, flip-chip micromirrors consistently demonstrate less than 2 nanometers of root-mean square surface roughness.
Flip chip bonding of two integrated circuit sized component modules into a MEMS or other single device has however almost universally required each of the component modules to remain on its fabrication substrate or a substitute substrate during the bonding operation. The known few exceptions to this rule involve especially fabricated modules affording some special form of protection for one module. The present invention changes this situation into one wherein someone with access to the most basic device fabrication capability and its tools can achieve flip chip bonded devices, including devices fabricated on two different and incompatible substrate materials and devices fabricated to include multiple MEMS modules in stacked array. Moreover the present invention eliminates a significant difficulty in correctly aligning two substrate-mounted modules for bonding. Since the present invention allows use of simple visual alignment procedures it eliminates the need for an expensive piece of measurement-capable fabrication equipment and need for the skilled user to operate this equipment. In direct terms, the present invention is thus concerned with improved off-substrate bonding.
The prior publication and patent art includes numerous examples of hinge and pivot arrangements used for erecting structural elements in an assembled MEMS device or as an active part of the MEMS device function. The concept of using a hinge or pivot as a key part of the assembly or fabrication procedure for a MEMS device, and especially for off chip rotation of substrate-free MEMS modules, appears however to be significantly less well known in the art. Several examples of prior art documents illustrating this state of the MEMS art are included in the references identified with the filing of the present document.
It is therefore an object of the present invention to provide a hinge-based arrangement through which simplified flip chip assembly can be accomplished.
It is another object of the present invention to provide a rotation based apparatus and procedure by which simplified flip-chip bonding can be accomplished.
It is another object of the invention to provide a lockable rotating hinge apparatus and method for assembling MEMS devices.
It is another object of the invention to provide a hinge arrangement that is operable by manual manipulation of hinge and associated latching elements.
It is another object of the present invention to provide a release, rotate, bond sequence for a flip-chip device.
It is another object of the invention to provide a latching hinge arrangement in which pivot pin and hinge clevis or hinge staple portions are achieved in integrated circuit size elements.
It is another object of the invention to provide for the non-wired rotation-based combination of incompatible process modules to form an Integrated Microsystem MEMS device.
It is another object of the invention to provide for the hinge-based combination of two or more low cost, perhaps incompatible, module fabrication processes to achieve a complex MEMS module.
It is another object of the invention to provide for the direct combination of a MEMS module with a CMOS module to form a CMOS MEMS device that is free of module interconnecting wiring.
It is another object of the present invention to provide a MEMS module fabrication arrangement in which multiple layers of MEMS elements may be stacked by rotation to form a complex MEMS device.
It is another object of the present invention to provide a MEMS device having two, three, four or more MEMS module layers that have been collected in a substrate free rotational alignment sequence.
It is another object of the present invention to provide an N layered flip-chip MEMS device.
It is another object of the present invention to provide a rotating hinge arrangement inclusive of provisions for convenient initial release of hinged elements from a sacrificial fabrication substrate member.
It is another object of the present invention to provide a procedure and apparatus in which all parts included in the upper layers of a hinge inclusive MEMS module are fully releasable during processing.
It is another object of the present invention to provide a procedure and apparatus in which a MEMS hinging and latching mechanism can be fabricated using only two uppermost and existing MEMS module layers in its composition.
It is another object of the present invention to provide a MEMS rotating hinge arrangement that is capable of large angle rotations.
It is another object of the present invention to provide a rotating hinge arrangement inclusive of rigid fixation apparatus for the rotated element.
It is another object of the present invention to provide a rotating hinge arrangement subject to fabrication in as few as two structural material layers.
It is another object of the present invention to provide a rotating hinge arrangement subject to fabrication in overlapping element form on a sacrificial substrate.
It is another object of the present invention to provide a rotating hinge arrangement providing a plurality of protections for a fragile, substrate-free, rotated MEMS module.
These and other objects of the invention will become apparent as the description of the representative embodiments proceeds.
These and other objects of the invention are achieved by the method of making a MEMS device comprising the steps of:
fabricating an array of MEMS modules and an array of MEMS controller modules on first and second fabrication substrate members;
a selected one of said array of modules having a sacrificial fabrication substrate member and including a plurality of connecting elements coupling said array of modules with a physically-stiffening header member;
each module of said MEMS array including an electromagnetic field-addressable physically movable active member;
each module of said MEMS controller array including an electromagnetic field-generating output member;
releasing said selected one of said array of modules from said sacrificial fabrication substrate member into a physically-stiffening header member-supported free state;
rotating said released selected one of said array of modules into an off substrate attached position of cantilever supporting by said connecting elements from said physically-stiffening header member;
aligning and bonding said released rotated array of modules with corresponding unreleased modules of said array of MEMS modules and array of MEMS controller modules to form an array of MEMS devices each having an electromagnetic field-addressable physically movable active member proximate an electromagnetic field-generating output member.